In the field of neurosurgery, when a patient with highly suspected smog is encountered, the doctor will recommend further DSA examination. Most patients have the question: Why do we need DSA when we have already done CT and MRA? Here is a detailed answer for you. Smoke disease is a rare disease discovered in Japan in the 1960s. Its name originated from the fact that the abnormal small blood vessels at the base of the skull were shaped like smoke when the patient underwent cerebral angiography. The essence of smog is a lesion of the blood vessels, which cannot be seen by the human eye. CT angiography (CTA), magnetic resonance angiography (MRA), and digital subtraction angiography (DSA) can be used to diagnose smog, and DSA is the gold standard for diagnosing smog. The difference between DSA, MRA and CTA is that MRA is a preliminary screening test for smog and other cerebrovascular diseases. The advantage of this technique is that it is non-invasive and can be done without contrast injection, and it can be performed at the same time as MRI. However, the resolution of MRA is poor in the examination of cerebrovascular diseases such as smog. CTA is a cerebrovascular imaging test done under a CT machine, which is also a non-invasive test technique and has improved resolution compared to MRA. However, unlike MRA, iodine-containing contrast agent needs to be injected during the examination. Before doing the examination, it is necessary to understand the patient’s kidney function because the contrast agent is excreted through the kidneys, and if the kidneys excrete well, not only can it be done quickly, but also can make the patient less painful. Digital subtraction angiography (DSA) is a high-end diagnostic technique that combines conventional angiography with computer technology. It is performed through a femoral artery cannula at the root of the thigh and is done under a digital subtraction angiography machine. DSA has high resolution and clear images, and it is recommended for patients who have been examined by MRA or CTA and are suspected of having smoldering disease to further confirm the diagnosis by DSA. Cerebral angiography (DSA) – the gold standard for the diagnosis of smog DSA is the gold standard for the diagnosis of smog. It not only provides a clear view of the morphological structure of the blood vessels in the brain, but also provides a true three-dimensional image of vascular lesions and the localization and measurement of vascular stenosis. It also shows the narrowing or occlusion of the main branches of the cerebral arterial ring and the abnormal network of small vessels like smoke at the base of the skull, providing an accurate and reliable basis for clinical diagnosis.